The Norway Rat is the largest of the commensal (living in close association with humans) rodents. The head and body are 7 to 10 inches long and the tail is an additional 6 to 8 inches. It has a stocky body and it weighs 7 to 18 ounces. The fur is coarse, shaggy and brown with some black hairs. The muzzle is blunt, eyes and ears are small and the tail which is bi-colored is shorter that the head and body combined. Adults are sexually mature in two to five months. Females produce three to six litters per year each averaging seven to eight young. Adults live from six to twelve months. They have poor sight but keen senses of smell, taste, hearing, and touch. Outdoors, Norway rats prefer to nest in burrows in the soil under sidewalks and concrete pads, stream/river banks, railroad track beds, next to buildings and in low ground cover. The rats easily enter buildings through ½ inch and larger gaps. In buildings they prefer to nest in the lower levels including crawlspaces, basements, loading docks, and sewers. Rats are associated with various diseases and occasionally bite. Leptospirosis is vectored by rats. This disease is acquired by eating food and drinking water which are contaminated with infected rat urine. Rats also cause significant structural damage and product destruction.
The House Mouse is the most common and economically important commensal rodent. The house mouse is gray and weighs ½ to one ounce. Its body is three to four inches long and the tail three to four inches long. The muzzle is pointed, the ears are large, the eyes and body are small. The female house mouse reaches sexual maturity in 35 days and averages eight litters per year, each of which averages six young. Thus, with 30 to 35 weaned mice per year populations build up rapidly. The mice typically produce their largest litters in the spring, depending on climatic conditions and begin to breed at dive to six weeks of age. The life span is one year.
The Roof Rat is a commensal rodent. The head and body are six to eight inches long and the tail is an additional seven to ten inches. It has a slight body which wigs five to nine ounces. The fur is soft, smooth and brown in color with some black hairs. The muzzle is pointed, eyes and ears are large and the scaly tail which is uniformly dark is longer that the head and body combined. Adults are sexually mature in two to five months. Females produce four to six litters per year each averaging six to eight young. Adults live from nine to twelve months. They have poor sight but keen senses of smell, taste hearing, and touch. Rats are nocturnal. They are shy about new objects and very cautious when things change in their environment and along their established runs. Roof rats prefer to nest in trees and occasionally in burrow and vegetation.